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Hoping someone may have run into this issue before and can shed some light...

I have been through 3 batteries in the last 6 months - all swollen with heavy corrosion on the negative battery lead.

My multimeter is telling me 13-14volts at the battery at idle and spiking to 14.9 - 15.4 when I rev it.

Putting the multimeter directly onto the positive alternator post I am only getting a max of 12.5volts - is this not too low for keeping the battery adequately charged? It does not fluctuate when I rev it...


Any thoughts?

Thanks much
 

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Sounds like the alternator is seriously overcharging while you're driving.
You can also do a voltage drop test on the cables to determine their health, they should be less the 1 volt on each.
If you have a decent local shop, they should do a basic battery alternator test for you, and that would be a bit more thorough then just a dvom reading.
 

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The JK has no regulator in the Alternator instead it is externally regulated by the PCM and poor ground connections can cause severe overcharging. Therefore check all your ground cables, especially the ones from/to the engine, battery and the PCM.
 

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Hoping someone may have run into this issue before and can shed some light...

I have been through 3 batteries in the last 6 months - all swollen with heavy corrosion on the negative battery lead.

My multimeter is telling me 13-14volts at the battery at idle and spiking to 14.9 - 15.4 when I rev it.

Putting the multimeter directly onto the positive alternator post I am only getting a max of 12.5volts - is this not too low for keeping the battery adequately charged? It does not fluctuate when I rev it...


Any thoughts?

Thanks much
14.9 - 15.4 volts is high enough to cause gassing, which will eventually run the battery dry.

The post above is on the right track regarding checking all your wires and connections. Most often sustained high charging voltage is caused by the computer not seeing the true battery voltage. It will crank up the alternator in an effort to make up for the low voltage, which, under normal circumstances, doesn't last long enough to harm the battery.
 

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The PCM fully controls the Alternator output via the "Gen Field" wire but as far as I know this is PWM therefore a duty cycle meter or oscilloscope would be needed to better analyze it.

P.S. your multimeter readings are not making any sense and you likely had a poor contact with your probes when you measured on the alternator ( well that's unless you have a second alternator installed somewhere :) )
 

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My 2016 JK is doing the same thing. Went through an Optima yellow top in 3 months. Today I noticed it's only charging to 13.5v.
 

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The JK has no regulator in the Alternator instead it is externally regulated by the PCM and poor ground connections can cause severe overcharging. Therefore check all your ground cables, especially the ones from/to the engine, battery and the PCM.



as ronjenx confirms, this above reply is on target ^.

Grounding of JK/JKU components is one of the most important troubleshooting & maintenance routines for this model. Being nearly completely " by wire" , the voltage being off to any great variance such as this is almost always undersuited, damage , worn or misconnected grounding wires.
replace or clean & reconnect the leads . The stock little terminal clamps suck on older JKs . Beef those up , too.



I'd be surprised if s new alternator didn't do the exact same thing. Go get one you can return & try it. That'd tell you a lot.

 

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